1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to driving a polarization switch, and more particularly, to driving a polarization switch to improve the quality of images displayed by a stereoscopic image display apparatus that includes a liquid crystal display (LCD) panel and a liquid crystal polarization switch.
2. Description of the Related Art
A polarization switch is a device for changing a polarization direction of incident light thereon based on electric control. Related art polarization switches include a transparent electro-optic layer provided between transparent substrates. For example, the electro-optic layer used in the polarization switch can be a liquid crystal layer.
FIG. 1 shows a schematic structure of a related art liquid crystal polarization switch 10. Referring to FIG. 1, the polarization switch 10 includes two transparent substrates 11 and 17, transparent electrodes 12 and 16 formed on surfaces of the substrates 11 and 17, respectively, which face each other, liquid crystal arrangement layers 13 and 15 which initially arrange the liquid crystal, and a liquid crystal layer 14 filled between the two transparent substrates 11 and 17. The polarization switch 10 with the above structure can be designed so that the polarization direction of light transmitted through the polarization switch 10 is not changed when a maximum voltage is applied to the transparent electrodes 12 and 16, and the polarization direction of the light transmitted through the polarization switch 10 is changed by a 90° angle when no voltage is applied to the transparent electrodes 12 and 16.
The polarization switch can be effectively used to provide left eye images and right eye images with different polarization directions from each other in a time-divisional stereoscopic image display apparatus. FIG. 2 shows an example of a polarizing eyeglasses-type time-divisional stereoscopic image display apparatus which includes the above polarization switch. The time-divisional stereoscopic image display apparatus displays left eye images and right eye images on the entire screen at very fast intervals, and at the same time, separately provides the left eye and the right eye with the images in synchronization with the display intervals of the left eye images and the right eye images. Referring to FIG. 2, the stereoscopic image display apparatus 20 includes a display panel 21 which displays images, a polarization plate 22, a polarization switch 23, a pulse generator 24 for driving the polarization switch 23, and polarizing eyeglasses 25.
The display panel 21 displays the left eye images and the right eye images alternately in frame units. The polarization plate 22 polarizes the image provided from the display panel 21 at a 45° angle. The polarization switch 23 does not change the polarization direction of the incident light when the voltage is applied, and changes the polarization direction of the incident light by a 90° angle when the voltage is not applied. The pulse generator 24 generates pulse signals that are synchronized with the displaying periods of the left eye images and the right eye images, and sends the pulse signals to the polarization switch 23. The polarizing eyeglasses 25 include a left eye polarizer 25a having a polarization direction at a 135° angle, and a right eye polarizer 25b having a polarization direction at a 45° angle.
In the above structure, while the display panel 21 displays the left eye image, a low level pulse is applied to the polarization switch 23. Then the light transmitted through the polarization plate 22 and the polarization switch 23 is polarized at a 135° angle, and the image is only transmitted through the left eye polarizer 25a of the polarizing eyeglasses 25. In addition, while the display panel 21 displays the right eye image, a high level pulse is applied to the polarization switch 23. Then the light transmitted through the polarization plate 22 and the polarization switch 23 is polarized at a 45° angle, and the image is transmitted only through the right eye polarization plate 25b of the polarizing eyeglasses 25.
The related art pulse generator 24 provides the polarization switch 23 with pulses with a 50% duty cycle. That is, when a period of the pulse supplied to the polarization switch 23 is T, the period with a high level (T1) and the period with a low level (T2) are each equal to T/2. However, a response speed when the liquid crystal transits from the low level to the high level is faster than a response speed when the liquid crystal transits from the high level to the low level. Therefore, where the polarization switch 23 and the display panel 21 both use the liquid crystal, the intensities of lights recognized by the left eye and the right eye are different from each other, and cross-talks recognized by the left eye and the right eye are different from each other.